Organopolysiloxane materials which can be cross-linked by cleaving alcohols into elastomers

ABSTRACT

The invention relates to a method for producing organopolysiloxane terminated with alkoxy groups, wherein A) organopolysiloxane terminated with HO is reacted with B) alkoxysilane having at least three alkoxy groups and/or whose partial hydrolysate is made to react in the presence of C) acid phosphoric acid ester of general formula (I): (HO) a OP(—O—[(CR 1   2 ) b —O] c [(CR 2   2 ) d ] e —L—M) (3−a) , wherein a=1 or 2; R 1  and R 2 =a hydrogen, methyl or hydroxyl radical; b and d=2 or 3; c=integral values from 2 to 15; e=0 or 1; L=a radical from the group —O—, —COO—, —OOC—, —CONR 3 —, —NR 4 CO— and —CO—; R 3  and R 4 =a hydrogen or a C 1 -C 10 -alkyl radical and M=a monovalent, optionally a hydroxyl, fluorine, chlorine, bromine, C 1 -C 10 -alkoxylalkyl or cyano group substituted C 1 - to C 20 -hydrocarbon radical, provided that the radicals R 1  and R 2  can only be at one given time a hydroxyl radical in each hydrocarbon atom. The invention further relates to RTV-1-alkoxy masses comprising the reaction product containing organopolysiloxane terminated with alkoxy groups as the essential constituent.

The invention relates to the preparation of alkoxy-terminatedorganopolysiloxane and to the use of this organopolysiloxane as aconstituent of alkoxy RTV1 compositions.

For the purposes of the present invention, the term organopolysiloxanesis intended to include dimeric, oligomeric and polymeric siloxanes.

Organopolysiloxane compositions which can be stored while moisture isexcluded and which crosslink when exposed to moisture at roomtemperature, with elimination of alcohols, are known as alkoxy RTV1compositions and have been known for a long time. They essentiallyconsist of organyloxy-terminated organopolysiloxane and, as otherconstituents, crosslinking agents having at least three hydrolyzablegroups, catalyst and, if desired, additives. The advantage of thesealkoxy RTV1 systems is that the alcohols released as cleavage productsduring the crosslinking are odorless, neutral and not harmful to theenvironment.

Alkoxy-terminated organopolysiloxane is prepared by reactingHO-terminated organopolysiloxane with alkoxysilanes. This is describedin U.S. Pat. No. 4,942,211, for example. A disadvantage of this processis that the reaction requires several hours at room temperature. Atelevated temperature although the reaction time is shortened it is stilllong enough for there to be some waiting time before thealkoxy-terminated organopolysiloxane formed can be used with otherconstituents to prepare alkoxy RTV1 compositions.

It is known that reactions of HO-terminated organopolysiloxane withalkoxysilanes can be accelerated by various catalysts. For exampleEP-A-763 557 carries out the reaction in the presence of acid dialkylphosphoric esters. The dialkyl phosphates have to be deactivated bybases after their reaction, since otherwise the alkoxy-terminatedorganopolysiloxanes become depolymerized and loose their crosslinkingcapability.

The object on which the invention is based is to find a very simple wayof preparing alkoxy-terminated organopolysiloxane for alkoxy RTV1compositions.

The invention provides a process for preparing alkoxy-terminatedorganopolysiloxane, in which

(A) HO-terminated organopolysiloxane is reacted with

(B) alkoxysilane which has at least three alkoxy groups and/or itspartial hydrolysates, in the presence of

(C) acid phosphoric ester of the general formula (I)

(HO)_(a)OP(—O—[(CR¹ ₂)_(b)—O]_(c)(CR²)_(d)—L—M)_((3−a))

where

a is 1 or 2,

R¹ and R² are a hydrogen radical, methyl radical or hydroxyl radical,

b and d are 2 or 3,

c is an integer from 2 to 15,

L is a radical selected from the class consisting of —O—, —COO—, —OOC—,—CONR³—, —NR⁴CO— and —CO—,

R³ and R⁴ are a hydrogen radical or C₁-C₁₀-alkyl radical, and

M is a monovalent, unsubstituted or hydroxyl-, fluorine-, chlorine-,bromine-, C₁-C₁₀-alkoxyalkyl- or cyano-substituted C₁-C₂₀-hydrocarbonradical, with the proviso that on any carbon atom only one radical R¹and R² may be a hydroxyl radical.

The process runs at temperatures as low as room temperature with anextremely high rate of reaction and selectively, and thereforeimmediately after mixing components (A), (B) and (C), thealkoxy-terminated organopolysiloxane formed can be used as an alkoxyRTV1 composition, if desired after admixing other constituents. There isno need to check whether the reaction has run to completion.

Another advantage of this process is that no side-reactions occur and,for example, no formation of T units or Q units is observed on a linearorganopolysiloxane.

The acid phosphoric esters (C) do not have to be deactivated immediatelyafter the reaction.

c is preferably an integer from 2 to 10, in particular 2, 3, 4 or 5. Lis preferably an —O— radical. M is preferably an unsubstituted orC₁-C₁₀-alkoxyalkyl-substituted C₁-C₂₀-hydrocarbon radical, in particularan unsubstituted C₅-C₁₈-hydrocarbon radical. R¹ and R² are preferably ahydrogen radical. b and d are preferably 2.

The HO-terminated organopolysiloxanes (A) used are preferably linear α,ω-dihydroxypoly(diorganosiloxanes) of the general formula (II)

HO—[(R₂SiO]_(m)—H  (II),

where

R is a monovalent, unsubstituted or fluorine-, chlorine-,bromo-C₁-C₄-alkoxyalkyl- or cyano- substituted C₁-C₈-hydrocarbonradical, and

m has a value which corresponds to a viscosity of the HO-terminatedorganopolysiloxane (A) of from 0.05 to 1000 Pa.s.

Examples of hydrocarbon radicals R are linear and cyclic, saturated andunsaturated; alkyl radicals, such as the methyl radical, aryl radicals,such as the phenyl radical, alkaryl radicals, such as tolyl radicals,and aralkyl radicals, such as the benzyl radical.

Preferred radicals R are unsubstituted hydrocarbon radicals having from1 to 6 carbon atoms, particularly preferably the methyl radical.

The organopolysiloxanes (A) preferably have a viscosity of from 100 to700,000 mPa.s, in particular from 20,000 to 350,000 mPa.s, measured ineach case at 23° C.

The alkoxysilanes (B) preferably have the general formula (III)

R⁵ _(μ)Si (OR⁶)_(4−μ)  (III),

where

R⁵ and R⁶ are monovalent, unsubstituted or fluorine-, chlorine-,bromine-, C₁-C₄-alkoxyalkyl- or cyano-substituted C₁-C₁₃-hydrocarbonradicals, and

μ is 0 or 1.

The partial hydrolysates of alkoxysilane (B) have been produced byhydrolyzing and condensing in particular from 2 to 4 alkoxysilanes.Examples of partial hydrolysates (B) are hexamethoxydisiloxane andhexa-ethoxydisiloxane.

Each of R⁵ and R⁶ is preferably an unsubstituted C₁-C₆-hydrocarbonradical, in particular a methyl, ethyl or propyl radical.

The acid phosphoric esters (C) of the general formula (I) arestorage-stabilizers for the alkoxy RTV1 compositions prepared from thealkoxy-terminated organopolysiloxane. In particular, the skin formationtimes of the alkoxy RTV1 compositions remain virtually constant andstable, and discoloration is suppressed.

In the general formulae (I) to (III), all of the radicals R and R¹ toR⁸, and all of the indices a, b, c, d, e, m and μ, are identical ordifferent, independently of one another.

In all of the formulae the silicon atom is tetravalent. For example, n+ois not more than 4.

The amounts of the acid phosphoric esters (C) used, based on 500 partsby weight of the HO-terminated organopolysiloxanes (A) are from 0.1 to50 parts by weight, in particular from 2 to 20 parts by weight.

The alkoxysilanes (B) are preferably added in excess to theHO-terminated organopolysiloxanes (A) in terms of the stoichiometricratios. In order to permit the reaction of the HO-terminatedorganopolysiloxanes (A) with alkoxysilanes (B) to run as far as possibletoward completion, use may preferably be made of from 10 to 60 parts byweight, in particular from 20 to 50 parts by weight, of thealkoxysilanes (B) per 500 parts by weight of the HO-terminatedorganopolysiloxanes (A). The excess of alkoxysilanes (B) not consumedduring the reaction is not disadvantageous in the organyloxy-terminatedorgano-polysiloxane and in the alkoxy RTV1 compositions, and maytherefore remain in the product of the reaction. An excess ofalkoxysilanes (B) acts as crosslinking component in the alkoxy RTV1compositions.

The reaction preferably takes place at temperatures of from +20 to +50°C., in particular at room temperature. Depending on the alkoxysilane (B)used, the reaction time is from 1 to 10 minutes.

The rate of the reaction depends firstly on the reactivity of thealkoxysilane (B) used and secondly on the acid phosphoric ester (C).

At room temperature the particularly preferred duration of the reactionis from 2 to 5 min, and this is specifically an advantage for preparingRTV1 compositions by the one-pot process.

The invention also relates to alkoxy RTV1 compositions which comprisethe reaction product prepared by the abovementioned process, in which asubstantial constituent is alkoxy-terminated organopolysiloxane.

In addition to the abovementioned components, the alkoxy RTV1compositions may comprise other components known per se.

Other substances which may preferably be added when preparing the alkoxyRTV1 compositions are bis-(trialkoxysilyl)-C₁-C₁₂ alkanes in which thealkoxy radicals are OR⁶, for example bis(triethoxysilyl)ethane.

In preparing the alkoxy RTV1 compositions use may also be made ofcondensation catalysts, reinforcing fillers, nonreinforcing fillers,pigments, soluble dyes, fragrances, plasticizers, phosphoric esters ordimethylpolysiloxanes end-capped by trimethylsiloxy groups and liquid atroom temperature, fungicides, resin-like organopolysiloxanes, includingthose composed of (CH₃)₃SiO_(1/2) units and SiO_(4/2) units, purelyorganic resins, such as homo- or copolymers of acrylonitrile, ofstyrene, of vinyl chloride or of propylene, where purely organic resinsof this type, in particular copolymers of styrene and n-butyl acrylate,may have been produced by free-radical polymerization of the monomersmentioned in the presence of diorganopolysiloxane having an Si-bondedhydroxyl group in each terminal unit, corrosion inhibitors,poly-glycols, which may have been esterified and/or etherified,oxidation retarders, heat stabilizers, solvents, agents to affect theelectrical properties, such as conductive carbon black, flameretardants, light stabilizers and agents to prolong skin-formation time,such as silanes having SiC-bonded mercaptoalkyl radicals, and alsoblowing agents, e.g. azodicarbonamide. Other substances which may beadded are adhesion promoters, preferably aminoalkyl-functional silanes,such as γ-aminopropyltriethoxysilane.

It is preferable to use condensation catalysts. The alkoxy RTV1compositions may according to the invention comprise any desiredcondensation catalysts among those which have been present hitherto incompositions which can be stored while water is excluded and whichcrosslink when exposed to water at room temperature to give elastomers.

Examples of condensation catalysts of this type are organic compounds oftin, zinc, zirconium, titanium or aluminum. Of these condensationcatalysts, preference is given to butyl titanates and organic tincompounds, such as di-n-butyltin diacetate and di-n-butyltin dilaurate,and to products of the reaction of a diorganotin diacylate with asilane, each molecule of which has, as hydrolyzable groups, at least twomonovalent hydrocarbon radicals which have bonding via oxygen to siliconand if desired have alkoxy substitution, or with oligomers of the same,where the tin atoms in the products of this reaction have all of theirvalences satisfied by oxygen atoms in the group ≡SiOSn≡ and/or bySnC-bonded, monovalent organic radicals.

The alkoxy RTV1 compositions preferably comprise fillers. Examples offillers are nonreinforcing fillers, i.e. fillers with a BET surface areaof up to 50 m²/g, such as quartz, diatomaceous earth, calcium silicate,zirconium silicate, zeolites, metal oxide powders, such as aluminumoxides, titanium oxides, iron oxides or zinc oxides and/or mixed oxidesof these, barium sulfate, calcium carbonate, gypsum, silicon nitride,silicon carbide, boron nitride, powdered glass and powdered plastics,such as powdered polyacrylonitrile; reinforcing fillers, i.e. fillerswith a BET surface area of more than 50 m²/g, such as fumed silica,precipitated silica, carbon black, such as furnace black or acetyleneblack, and silicon-aluminum mixed oxides of high BET surface area; andfibrous fillers, such as asbestos and synthetic polymeric fibers.

The fillers mentioned may have been hydrophobicized, for example bytreatment with organosilanes and/or -siloxanes or with stearic acid, orby etherifying hydroxyl groups to give alkoxy groups. It is possible touse one type of filler, or else a mixture of at least two fillers.

If reinforcing silica is used as sole filler it is possible to preparetransparent alkoxy RTV1 compositions.

The usual moisture present in the air is sufficient to crosslink thealkoxy RTV1 compositions. If desired, it is also possible for thecrosslinking to be carried out at temperatures below or above roomtemperature, e.g. at from −5 to 10° C., or at from 30 to 50° C.

The novel alkoxy RTV1 compositions therefore have excellent suitabilityas, for example, compositions for sealing joints, including joints whichrun vertically, or for sealing spaces of, for example, clear width from10 to 40 mm, e.g. in buildings, land vehicles, watercraft or aircraft,or as adhesives or putties, e.g. in the construction of windows or theproduction of display cabinets, and also, for example, for theproduction of protective coatings, or of elastomeric moldings, or alsofor the insulation of electrical or electronic equipment.

In the examples described below, all data on percentage parts are basedon weight unless otherwise stated. All viscosity data moreover are basedon a temperature of 25° C. Unless otherwise stated the examples beloware carried out at ambient atmospheric pressure, i.e. at about 1000 hPa,and at a room temperature, i.e. at about 20° C., at [sic] a temperaturewhich results when the reactants are brought together at roomtemperature without additional heating or cooling.

EXAMPLES Example 1

500 g of a dimethylpolysiloxane which has a hydroxyl group in eachterminal unit and has a viscosity of 80,000 mPa.s at 23° C. are mixed,in a planetary mixer which can operate under vacuum, with 350 g of apolydimethylsiloxane having trimethylsiloxy groups in the terminal unitsand having a viscosity of 100 m²/s (23° C.) and 10 g of a mixture ofalkoxylated phosphoric esters of the formulae

(OH)₁PO[(OCH₂CH₂)₃₋₄—O—(CH₂)₁₁₋₁₄—CH₃]₂.

and

(OH)₁PO[(OCH₂CH₂)₃₋₄—O—(CH₂)₁₁₋₁₄—CH₃]₁.

25 g of methyltrimethoxysilane are then immediately added in a singleportion, followed by homogenization in vacuo for 5 minutes. Thefollowing are then added in the sequence given, using the mixingtechniques usual for RTV1 compositions:

13.5 g of γ-aminopropyltriethoxysilane, 80.0 g of hydrophilic fumedsilica with a BET surface area of 150 m²/g and 5.0 g of a reactionproduct prepared by heating a mixture of 4 parts of tetraethyl silicateand 2.2 parts of di-n-butyltin diacetate for 6 hours at 120° C. atambient atmospheric pressure, with stirring, and at the same timedistilling off the ethyl acetate produced.

After homogenization in vacuo, the compound is drawn off intomoisture-proof packs. Specimens are taken at various intervals and theskin-formation times (at 23° C./50% relative humidity) determined forthe elastomers prepared from these. The results achieved here are listedin Table 1.

The following mechanical properties of the elastomers were determined:

Shore A: 10; ultimate tensile strength: 1.0 N/mm²; elongation at break:560%; tear propagation resistance: 2.7 N/mm; Stress at 100% elongation:0.2 N/mm².

Example 2

The procedure is similar to that of Example 1. To 600 g of theα,ω-dihydroxypolydimethylsiloxane of Example 1, the followingingredients are added in the sequence given:

280.0 g of polydimethylsiloxane having —Si(CH₃)₃ end groups

10.0 g of alkoxylated phosphoric esters of Example 1

25.0 g of vinyltrimethoxysilane,

15.0 g of γ-aminopropyltriethoxysilane,

70.0 g of hydrophilic fumed silica with a BET surface area of 150 m²/gand

5.0 g of the reaction product from tetraethyl silicate and di-n-butyltindiacetate of Example 1.

The skin-formation times of the elastomers prepared therefrom are listedin Table 1.

Example 3

The procedure is similar to that of Example 1. The following ingredientsare admixed in the sequence given with 500 g of theα,ω-dihydroxypolydimethylsiloxane:

380.0 g of polydimethylsiloxane having —Si(CH₃)₃ end groups,

10.0 g of the alkoxylated phosphoric ester of Example 1,

25.0 g of methyltrimethoxysilane,

10.0 g of 3-(2-aminoethylamino)propyltrimethoxysilane,

70.0 g of hydrophilic fumed silica with a BET surface area of 150 m²/g,and

4.0 g of the reaction product of tetraethyl silicate and di-n-butyltindiacetate from Example 1.

The skin-formation times of the elastomers prepared therefrom are listedin Table 1.

Example 4

The procedure is similar to that of Example 1.

500.0 g of α,ω-dihydroxypolydimethylsiloxane of Example 1,

380.0 g of polydimethylsiloxane having —Si(CH₃)₃ end groups,

10.0 g of alkoxylated phosphoric ester of Example 1,

25.0 g of methyltrimethoxysilane,

8.0 g of γ-aminopropyltriethoxysilane,

70.0 g of hydrophilic fumed silica with a BET surface area of 150 m²/gand

4.0 g of the reaction product from tetraethyl silicate and di-n-butyltindiacetate of Example 1 are mixed.

The skin-formation times of the elastomers produced therefrom are listedin Table 1.

Example 5

The procedure is similar to that of Example 1. The following are mixed:

500.0 g of the α,ω-dihydroxypolydimethylsiloxane of Example 1

380.0 g of polydimethylsiloxane having —Si(CH₃)₃ end groups,

10.0 g of the alkoxylated phosphoric ester of Example 1,

25.0 g of vinyltrimethoxysilane,

25.0 g of amino-functional siloxane: equilibration product made fromaminopropyltriethoxysilane and from a condensate/hydrolysate ofmethyltriethoxysilane with an amine number of 2.2,

70.0 g of hydrophilic fumed silica with a BET surface area of 150 m²/gand

5.0 g of the reaction product of tetraethyl silicate and di-n-butyltindiacetate from Example 1.

The skin-formation times of the elastomers produced therefrom are listedin Table 1.

TABLE 1 Storage time while moisture Example 1 Example 2 Example 3Example 4 Example 5 is excluded RT 50° C. RT 50° C. RT 50° C. RT 50° C.RT 50° C.  7 d 17 min 20 min 15 min 20 min 10 min 10 min 40 min 42 min15 min 25 min 14 d 18 min 20 min 17 min 25 min 10 min 12 min 38 min 45min 16 min 35 min 21 d 20 min 25 min 18 min 30 min 14 min 17 min 35 min50 min 15 min 30 min

Example 6

600 g of a polydimethylsiloxane which has a hydroxyl group in eachterminal unit and has a viscosity of 80,000 mPa.s at 23° C., 300 g of apolydimethylsiloxane having trimethylsiloxy groups as terminal units andhaving a viscosity of 100 mm²/s at 23° C., and also 10 g of thealkoxylated phosphoric ester of Example 1 are mixed homogeneously in aplanetary mixer which can operate under vacuum. 35 g ofmethyltrimethoxysilane are then immediately added, followed by furtherthomogenization for 5 minutes. The following ingredients are then addedstepwise in succession to this premix, while the mixing techniqueremains that which is usual for RTV1 compositions:

15.0 g of γ-aminopropyltriethoxysilane,

70.0 g of hydrophilic fumed silica with a BET specific surface area of150 m²/g, and

5.0 g of the reaction product of tetraethyl silicate and di-n-butyltindiacetate from Example 1.

After homogenization at reduced pressure, the compound is drawn off intomoisture-proof packs. After storage for 1 day at room temperature theskin-formation time is determined as 10 minutes (23° C./50% relativehumidity). After a further 7 days of storage at 50° C. theskin-formation time is 15 minutes.

Example 7

Example 6 is repeated. However, the other ingredients added in amodified sequence to a premix of the same make-up are:

70.0 g of hydrophilic fumed silica with a BET specific surface area of150 m²/g,

15.0 g of γ-aminopropyltriethoxysilane and

5.0 g of the reaction product of tetraethyl silicate and di-n-butyltindiacetate from Example 1.

After homogenization at reduced pressure, the compound is drawn off intomoisture-proof packs. After storage at room temperature for 1 day theskin-formation time is determined as 12 minutes (23° C./50% relativehumidity). After an additional 7 days of storage at 50° C. theskin-formation time is 15 minutes.

Example 8

Example 6 is repeated. Further ingredients are added as follows to apremix of the same make-up:

70.0 g of a hydrophilic fumed silica with a specific BET surface area of150 m²/g and

5.0 g of the reaction product from tetraethyl silicate and di-n-butyltindiacetate of Example 1.

After homogenization at reduced pressure the compound is allowed tostand for 3 hours while moisture is excluded, and 15 g ofγ-aminopropyltriethoxysilane are then incorporated by mixing. After afurther homogenization at reduced pressure the compound is drawn offinto moisture-proof packs. After storage at room temperature for 1 daythe skin-formation time is determined as 12 minutes (23° C./50% relativehumidity). After an additional 7 days of storage at 50° C. theskin-formation time is 15 minutes.

Example 6 to 8 show that the sequence of addition of theγ-aminopropyltriethoxysilane coupling agent has no significant effect onthe skin-formation time. It is therefore not necessary for thealkoxylated phosphoric ester to be neutralized immediately by the basiccoupling agent.

Example 9

550 g of a polydimethylsiloxane having terminal hydroxyl groups and aviscosity of 80,000 mPa.s at 23° C., 325 g of a polydimethylsiloxanehaving terminal trimethylsiloxygroups, 50 g of methyltrimethoxysilaneand 10 g of the alkoxylated phosphoric ester of Example 1 arehomogeneously mixed, while water is excluded, in a planetary mixer whichcan operate under vacuum. After about 10 minutes the followingingredients are added and mixed homogeneously into the overallcomposition:

15.0 g of γ-aminopropyltriethoxysilane,

73.0 g of hydrophilic fumed silica with a BET surface area of 150 m²/g,

5.0 g of the reaction product from tetraethyl silicate and di-n-butyltindiacetate of Example 1 and

200.0 g of ground chalk treated with stearic acid.

After storage for 1 day at room temperature the skin-formation time isdetermined as 15 minutes. After a further 7 days of storage at 50° C.the skin-formation time was determined as 20 minutes.

Example 10

Example 9 was repeated but with the modification that the ground,stearic-acid-treated chalk was replaced by the same amount of untreatedground chalk. After 1 day of storage at room temperature theskin-formation time was determined as 20 minutes, and after a further 7days of storage at 50° C. the skin-formation time was determined as 25minutes.

Example 11

Example 9 was repeated, but with the modification that only 50 g ofhydrophilic fumed silica with a BET surface area of 150 m²/g were usedinstead of 73 g, and that the 200 g of ground chalk treated with stearicacid were replaced by the same amount of precipitated chalk treated withstearic acid and having a surface area of 19 m²/g. After storage for 1day at room temperature, the skin-formation time was determined as 15minutes, and after a further 7 days of storage at 50° C. theskin-formation time was 25 minutes.

Example 12

The procedure was similar to that of Example 1.

95.3 g of α,ω-dihydroxypolydimethylsiloxane of Example 1  1.2 g ofalkoxylated phosphoric ester of Example 1 and  3.5 g ofmethyltrimethoxysilane

were mixed in the sequence given above.

The viscosities of the mixture were measured:

after 1 h 64,000 mPa · s after 2 h 62,400 mPa · s after 3 h 60,800 mPa ·s

Example 13 Comparative Example

The procedure is similar to that of Example 1.

95.3 g of α,ω-dihydroxypolydimethylsiloxane of Example 1  1.2 g ofdi-2-ethylhexyl phosphate (as in EP-A-763 557) and  3.5 g ofmethyltrimethoxysilane

were mixed in the sequence given above.

The viscosities of the mixture were measured:

after 1 h 32,000 mPa · s after 2 h 12,000 mPa · s after 3 h 2000 mPa · s

Di-2-ethylhexyl phosphate depolymerizes the alkoxy-terminatedorganopolysiloxane.

What is claimed is:
 1. A process for preparing alkoxy-terminatedorganopolysiloxanes, comprising reacting (A) at least one HO-terminatedorganopolysiloxane (B) at least one alkoxysilane of the general formula(III) R⁵ _(μ)Si(OR⁶)_(4−μ)  (III), where R⁵ and R⁶ are independentlymonovalent, unsubstituted or fluorine-, chlorine-, bromine-,C₁-C₄-alkoxyalkyl- or cyano-substituted C₁-C₁₃-hydrocarbon radicals, andis 0 or 1, μ is 0 or 1, and/or a partial hydrolysate thereof, in thepresence of (C) at least one acid phosphoric ester of the generalformula (I) (HO)_(a)OP(—O—[(CR¹ ₂)_(b)—O]_(c)(CR²₂)_(d)—L—M)_((3−a))  (I), where a is 1 or 2, R¹ and R² are a hydrogenradical, methyl radical or hydroxyl radical, b and d are 2 or 3, c is aninteger from 2 to 15, L is a radical selected from the group consistingof —O—, —COO—, —OOC—, —CONR³—, —NR⁴CO— and —CO—, R³ and R⁴ areindependently a hydrogen radical or C₁-C₁₀-alkyl radical, and M is amonovalent, unsubstituted or hydroxyl-, fluorine-, chlorine-, bromine-,C₁-C₁₀-alkoxyalkyl- or cyano-substituted C₁-C₂₀-hydrocarbon radical,with the proviso that on any carbon atom only one radical R¹ and R² maybe a hydroxyl radical.
 2. A process as claimed in claim 1, in which theHO-terminated organopolysiloxane (A) used comprises linearα,ω-dihydroxypoly(diorgano)siloxanes of the general formula (II)HO—[R₂SiO]_(m)—H  (II), where R is a monovalent, unsubstituted orfluorine-, chlorine-, bromo-C₁-C₄-alkoxyalkyl- or cyano-substitutedC₁-C₈-hydrocarbon radical, and m has a value which corresponds to aviscosity of the HO-terminated organopolysiloxane (A) of from 0.05 to1000 Pa·s.
 3. The process of claim 1, wherein c is from 2 to 10, l is—O—, and m is an unsubstituted or C₁-C₂₀ hydrocarbon radical.
 4. Theprocess of claim 3, wherein c is from 2 to 5, R¹ and R² are H, and b andd are
 2. 5. The process of claim 1 wherein said acid phosphoric ester(C) comprises a mixture of (C)(1) (HO)PO[(OCH₂CH₂)₃₋₄—O—(CH₂)₁₁₋₁₄—CH₃]₂and (C)(2) (HO)₂PO[(OCH₂CH₂)₃₋₄—O—(CH₂)₁₁₋₁₄—CH₃].
 6. An alkoxy RTV1composition which comprises the reaction product of claim
 2. 7. Thealkoxy RTV1 composition of claim 6 wherein said acid phosphoric ester isnot separated from the reaction product.
 8. The alkoxy RTV1 compositionof claim 6 in which said acid phosphoric ester comprises a mixture of(C)(1) (HO)PO[(OCH₂CH₂)₃₋₄—O—(CH₂)₁₁₋₁₄—CH₃]₂ and (C)(2)(HO)₂PO[(OCH₂CH₂)₃₋₄—O—(CH₂)₁₁₋₁₄—CH₃].
 9. The alkoxy RTV-1 compositionof claim 6, further comprising a reinforcing filler having a BET surfacearea greater than 50 m²/g, optionally a non-reinforcing filler having aBET surface area of 50 m²/g or less, at least one aminoalkyl andalkoxy-functional silane, and a condensation catalyst.
 10. The alkoxyRTV-1 composition of claim 9, wherein said aminoalkyl andalkoxy-functional silane comprises γ-aminopropyltriethoxysilane.
 11. Thealkoxy RTV-1 composition of claim 9, wherein said condensation catalystcomprises the reaction product obtained by heating a mixture oftetraethylsilicate and di-n-butyltin diacetate while removing ethylacetate by distillation.
 12. The alkoxy RTV-1 composition of claim 9,wherein said aminoalkyl and alkoxy-functional silane comprises3-(2-aminoethylamino)propyltrimethoxysilane.